Bring the preview GH action into the product

[humitos]

We discussed about migrating the preview GH action into the product itself. The user should be able to mark Add link to preview in the pull request with comment and description as options.

I think we will need to use use the SocialAccount from one of the owners to put the link in the pull request as a comment or editing the description because we don't have a GitHub App for Read the Docs. We will need to research a little more here.

Note there are reason why most of these bots use a new comment, so we should probably use that approach only. Example, the content added to the description ends up in the commit message --which is something we don't want.

Sentry comment's example: #11765 (comment)

[agjohnson]

This would be good to start to figure out. Some things to explore:

• Is GHA required?
• Can we use a GHA in addition to our normal Oauth application, not changing authentication/authorization on our side yet?